When using the "section" parameter to the InsertPage plugin, the sections are delimited with horizontal rule lines. In the wiki markup source, the minimal number of hyphens to create a rule line is 4, I believe, but it is OK to use more hyphens. Any number greater than or equal to 4 creates the HR line.
Unfortunately, the InsertPage plugin with the "section" parameter eats EXACTLY 4 hyphens and copies the rest into the output, leaving meaningless marks in the visible wiki page.
The only workaround is to go through your source pages and make sure your users typed EXACTLY 4 hyphens where they wanted section breaks. Not pleasant.